[Does modification of documentation result in a reduction of medication to involuntary patients?]

OBJECTIVE

The effects of modification of documentation on the administration of psychotropic medication to involuntary patients in hospital were investigated.

METHODS

The charts of 414 inpatients on the acute-ward were reviewed two months before and two months after a new form for documentation of rationales for medication administration to involuntary patients was instituted. A follow-up was carried out for a two-month period a year later.

RESULTS

The percentage of patients who received medication involuntarily, 70% of whom were schizophrenic, fell by over half, from 12% to 5%, after additional standardized documentation for the use of such medications was instituted. The number of medications administered to involuntary patients fell from 80 to 21, a reduction of 74%. The effects were stable over the course of one year.

CONCLUSIONS

Modification of documentation seems to reduce the use of medication with involuntary patients.

[Type 2 diabetes and beta cell apoptosis]

Type 2 diabetes mellitus features an asymptomatic insulin resistance phase preceding the onset of diabetes. Hyperglycemia occurs when a relative insulin deficiency appears, meaning that beta cell secretory dysfunction is a key element in type 2 diabetes pathophysiology. So far, insulin secretion deficiency is explained by pancreatic beta cell "exhaustion" phenomena. Recent data suggest that apoptotic mechanisms could explain insulin deficiency through a reduction in the absolute pancreatic beta cell number. Psammomys obesus (sand rat) is an animal model for type 2 diabetes mellitus, initially characterized by hyperinsulinism followed by insulin deficiency linked with a reduction in the number of pancreatic beta cells. Transition to diabetes can be observed following changes in usual lifestyle of the sand rat. In the desert, caloric intake is low and physical expenditure is heavy. In the laboratory, animals turn diabetic as early as 4 days following a high calorie diet. At a later stage, diabetes is irreversible and animals die from diabetic ketoacidosis. beta cell apoptosis rate is low in non diabetic animals and increases 14-fold by 20 days after diabetes onset. At this stage, cells undergoing apoptosis can be observed, coexisting with necrotic cells without any insulitis. Similar results were obtained in vitro in isolated pancreatic islets that were exposed to increasing glucose concentrations, suggesting that chronic hyperglycemia plays a role in the onset or the deterioration of the process. However, precise mechanisms of apoptosis in this case remain poorly understood. Aminoguanidin does not prevent beta cell apoptosis in vitro, suggesting that advanced glycation products or NO production are not involved in this beta cell destruction process. Similar mechanisms secondary to hyperglycemia could play a role in the diabetes process in man and explain the marked insulin secretory deficiency that is sometimes observed in these patients. In addition to its preventing role on diabetes complication, the obtention of normoglycemia could help maintaining beta cell function.

Pancreatic and duodenal homeobox gene 1 induces expression of insulin genes in liver and ameliorates streptozotocin-induced hyperglycemia

Insulin gene expression is restricted to islet beta cells of the mammalian pancreas through specific control mechanisms mediated in part by specific transcription factors. The protein encoded by the pancreatic and duodenal homeobox gene 1 (PDX-1) is central in regulating pancreatic development and islet cell function. PDX-1 regulates insulin gene expression and is involved in islet cell-specific expression of various genes. Involvement of PDX-1 in islet-cell differentiation and function has been demonstrated mainly by 'loss-of-function' studies. We used a 'gain-of-function' approach to test whether PDX-1 could endow a non-islet tissue with pancreatic beta-cell characteristics in vivo. Recombinant-adenovirus-mediated gene transfer of PDX-1 to the livers of BALB/C and C57BL/6 mice activated expression of the endogenous, otherwise silent, genes for mouse insulin 1 and 2 and prohormone convertase 1/3 (PC 1/3). Expression of PDX-1 resulted in a substantial increase in hepatic immunoreactive insulin content and an increase of 300% in plasma immunoreactive insulin levels, compared with that in mice treated with control adenovirus. Hepatic immunoreactive insulin induced by PDX-1 was processed to mature mouse insulin 1 and 2 and was biologically active; it ameliorated hyperglycemia in diabetic mice treated with streptozotocin. These data indicate the capacity of PDX-1 to reprogram extrapancreatic tissue towards a beta-cell phenotype, may provide a valuable approach for generating 'self' surrogate beta cells, suitable for replacing impaired islet-cell function in diabetics.

Impaired beta-cell functions induced by chronic exposure of cultured human pancreatic islets to high glucose

In type 2 diabetes, chronic hyperglycemia has been suggested to be detrimental to beta-cell function, causing reduced glucose-stimulated insulin secretion and disproportionately elevated proinsulin. In the present study, we investigated the effect on several beta-cell functions of prolonged in vitro exposure of human pancreatic islet cultures to high glucose concentrations. Islets exposed to high glucose levels (33 mmol/l) for 4 and 9 days showed dramatic decreases in glucose-induced insulin release and in islet insulin content, with increased proportion of proinsulin-like peptides relative to insulin. The depletion in insulin stores correlated with the reduction in insulin mRNA levels and human insulin promoter transcriptional activity. We also demonstrated that high glucose dramatically lowered the binding activity of pancreatic duodenal homeobox 1 (the glucose-sensitive transcription factor), whereas the transcription factor rat insulin promoter element 3b1 activator was less influenced and insulin enhancer factor 1 remained unaffected. Most of these beta-cell impairments were partially reversible when islets first incubated for 6 days in high glucose were transferred to normal glucose (5.5 mmol/l) concentrations for 3 days. We conclude that cultured human islets are sensitive to the deleterious effect of high glucose concentrations at multiple functional levels, and that such mechanisms may play an important role in the decreased insulin production and secretion of type 2 diabetic patients.

Ion-assisted deposition of oxide materials at room temperature by use of different ion sources

Thin films of SiO(2), TiO(2), Ta(2)O(5), ZrO(2), and the mixed oxide H4 (Merck) have been deposited onto nonheated glass substrates by electron-beam evaporation in commercial coating plants. All depositions have been carried out with ion assistance provided by three different ion or plasma sources (end-hall, plasma, and cold-cathode sources). The optical film properties such as index of refraction, extinction coefficient, light scattering, and absorption have been examined by spectrophotometry, laser calorimetry, and total integrated light-scatter measurements. Surface morphology has been investigated by atomic force microscopy studies. Furthermore, films have undergone sand erosion tests for the determination of relative wear resistance. The film properties are compared for the three different ion sources.

Interaction between genetic and dietary factors determines beta-cell function in Psammomys obesus, an animal model of type 2 diabetes

The gerbil Psammomys obesus develops nutrition-dependent diabetes. We studied the interaction between diet and diabetic predisposition for beta-cell function. A 4-day high-energy (HE) diet induced a 3-, 4-, and 1.5-fold increase in serum glucose, insulin, and triglycerides, respectively, in diabetes-prone (DP) but not diabetes-resistant (DR) P. obesus. Hyperglycemia and concurrent 90% depletion of islet immunoreactive insulin stores were partially corrected by an 18-h fast. In vitro early insulin response to glucose was blunted in both DR and DP perifused islets. The HE diet augmented early and late insulin response in DR islets, whereas in DP islets, secretion progressively declined. Dose-response studies showed a species-related increase in islet glucose sensitivity, further augmented in DP P. obesus by a HE diet, concomitant with a decreased threshold for glucose and a 55% reduction in maximal response. These changes were associated with a fourfold increase in glucose phosphorylation capacity in DP islets. There were no differences in islet glucokinase (GK) and hexokinase (HK) Km; however, GK Vmax was 3.7- to 4.6-fold higher in DP islets, and HK Vmax was augmented 3.7-fold by the HE diet in DP islets. We conclude that the insulin-resistant P. obesus has an inherent deficiency in insulin release. In the genetically predisposed P. obesus (DP), augmented islet glucose phosphorylation ability and diet-induced reduction of the glucose threshold for secretion may lead to inadequate insulin secretion and depletion of insulin stores in the presence of caloric abundance. Thus, genetic predisposition and beta-cell maladaptation to nutritional load seem to determine together the progression to overt diabetes in this species. It is hypothesized that similar events may occur in obese type 2 diabetic patients.

Hyperglycemia-induced beta-cell apoptosis in pancreatic islets of Psammomys obesus during development of diabetes

The gerbil Psammomys obesus develops nutrition-dependent diabetes associated with moderate obesity. The disease is characterized by initial hyperinsulinemia, progressing to hypoinsulinemia associated with depleted pancreatic insulin stores. The contribution of changes in beta-cell turnover to insulin deficiency was investigated in vivo during transition to overt diabetes. Normo glycemic diabetes-prone P. obesus animals who were given a high-calorie diet developed hyperglycemia within 4 days, which was found to be associated with a progressive decline in pancreatic insulin content. This was accompanied by a transient increase in beta-cell proliferative activity and by a prolonged increase in the rate of beta-cell death, culminating in disruption of islet architecture. The hypothesis that "glucotoxicity" was responsible for these in vivo changes was investigated in vitro in primary islet cultures. Exposure of islets from diabetes-prone P. obesus to high glucose levels resulted in a dose-dependent increase in beta-cell DNA fragmentation. In contrast, high glucose levels did not induce DNA fragmentation in rat islets, whereas islets from a diabetes-resistant P. obesus line exhibited a reduced and delayed response. Aminoguanidine did not prevent glucose-induced beta-cell DNA fragmentation in vitro, suggesting that formation of nitric oxide and/or advanced glycation end products plays no major role. Elevated glucose concentrations stimulated beta-cell proliferation in both rat and P. obesus islets. However, unlike the marked long-lasting effect in rat islets, only a transient and reduced proliferative response was observed in P. obesus islets; furthermore, beta-cell proliferation was inhibited after prolonged exposure to elevated glucose levels. These results suggest that hyperglycemia-induced beta-cell death coupled with reduced proliferative capacity may contribute to the insulin deficiency and deterioration of glucose homeostasis in P. obesus. Similar adverse effects of hyperglycemia could play a role in the evolution of type 2 diabetes in genetically susceptible individuals.

Characterization of the unusual insulin of Psammomys obesus, a rodent with nutrition-induced NIDDM-like syndrome

Psammomys obesus fed a high-calorie diet develops a NIDDM-like syndrome. The use of reverse-phase high-performance liquid chromatography (HPLC) to study Psammomys insulin biosynthesis and release revealed a very delayed elution time for the Psammomys insulin peak appearing near the position of human proinsulin. This unusual peak was initially thought to represent partially processed insulin on the basis of its molecular size and susceptibility to trimming by carboxypeptidase B (CpB). However, the findings of an active carboxypeptidase E (CpE) enzyme and the normal amidated forms of gastrin and cholecystokinin octapeptide (CCK-8) in Psammomys tissues were inconsistent with CpE-related aberrant processing of insulin. Moreover, amino acid sequencing of the delayed peak of Psammomys insulin revealed fully processed insulin with amino acid sequence as predicted by the cDNA. The unique presence of a B-30 phenylalanine residue, resulting in an increased hydrophobicity of the insulin molecule, probably underlies the marked delay in elution time on HPLC. The unusual structure of Psammomys insulin does not appear to contribute to the proinsulinemia observed in diabetic Psammomys since the HPLC-purified molecule did not inhibit PC1 and PC2 convertase activities in an in vitro assay.

From sand rats to diabetic patients: is non-insulin-dependent diabetes mellitus a disease of the beta cell?

It has been debated for the past two decades whether non-insulin-dependent diabetes mellitus (NIDDM) is caused by insulin deficiency or insulin resistance. In this review we summarise the data which unequivocally indicate that insulin response to glucose is grossly deficient in patients with impaired glucose tolerance and NIDDM. Furthermore, we review the findings for Psammomys obesus (the sand rat), an animal with spontaneous obesity, insulin resistance and diabetes which has been used as the prototype for "hyperinsulinaemic NIDDM". A large proportion of circulating insulin in this animal consists of proinsulin and its split products, apparently resulting from hyperglycaemia-driven overstimulation of the beta cell, with depletion of its insulin stores. In vitro studies demonstrate that this "glucose toxic" effect can be reproduced in Psammomys islets but not in those of normal rats. This would indicate that increased demand for insulin production leads to aberrations in proinsulin production and processing only in beta cells with inherent (genetic?) defects. We also point to clinical findings which cast doubt on the practical importance of insulin resistance for the glucose homeostasis of NIDDM patients. In these cases, moderate doses of insulin administered by insulin pumps can induce near-normoglycaemia in NIDDM.

Near-infrared spectroscopy for monitoring water permeability of optical coatings on plastics

Near-infrared spectroscopy has been applied to determine the water content of plastic lenses. An analytical method is presented for monitoring the water permeability of thin layers on plastic optics by utilizing the reversible moisture absorption of organic polymers. As an example, scratch-resistant and antireflective layers on poly[diethylenglycol-bis(allylcarbonate)] lenses are investigated. The measurements demonstrate the relatively high water barrier of coatings deposited by plasma-ion-assisted deposition compared with classical physical vapor deposition coatings and polysiloxane dip coatings.

Substrate autoregulation of glucose transport: hexose 6-phosphate mediates the cellular distribution of glucose transporters

Exposure of rat skeletal muscle and skeletal muscle cell lines to high glucose levels results in a time- and dose-dependent reduction of the rate of hexose uptake, paralleled by a reduction in the plasma membrane density of glucose transporters. The mechanism of this process was investigated in cultured L8 myocytes. Low concentrations (0.5-2.0 mmol/l) of deoxyglucose mimicked the downregulatory action of 20 mmol/l glucose both regarding the time-course and magnitude of the effect, but in an irreversible manner. A dose-dependent relationship between intracellular accumulation of deoxyglucose 6-phosphate and the magnitude of the downregulatory response was observed. Depletion of intracellular deoxyglucose 6-phosphate restored the rate of hexose transport to the control level. The reduction of hexose transport activity by deoxyglucose occurred independently of ATP depletion which by itself produced the opposite effect. The effects of deoxyglucose and high glucose on hexose transport were associated with reduced transport maximal velocity and GLUT1 transporter abundance in the plasma membranes of myocytes, as assessed by cell surface biotinylation. The reduction of myocyte GLUT1 mRNA content, observed after exposure to high glucose, did not accompany the transport down regulatory action of deoxyglucose. We suggest that hexose 6-phosphate is the mediator of the downregulatory signal for subcellular redistribution of GLUT1 in L8 myocytes. The signal responsible for reducing the GLUT1 mRNA level may be related to glucose metabolites downstream of the hexokinase reaction.

Increased susceptibility of islets from diabetes-prone Psammomys obesus to the deleterious effects of chronic glucose exposure

Patients with noninsulin-dependent diabetes (NIDDM) show an increase in the relative plasma levels of proinsulin and proinsulin conversion intermediates, which is corrected by strict glycemic control. This observation suggests that hyperglycemia per se may be responsible for generating the aberrant plasma hormone profile. The question remains, however, whether a genetic predisposition to NIDDM underlies the failure of the insulin production machinery to meet a prolonged increase in secretory demand. In this study, islet monolayer cultures from the diabetes-prone Psammomys obesus and normal diabetes-resistant rats were exposed to RPMI 1640 medium containing either 11.1 or 33.3 mM glucose; insulin-related peptides were resolved by HPLC. Prolonged exposure (10 days) of rat islets to high glucose resulted in a reduced a secretory response to an acute glucose stimulus associated with a 37% reduction in the insulin content but no change in the proinsulin/insulin ratio. When subjected to a similar protocol, islets from prediabetic Psammomys lost the insulin response to glucose; beta-cell insulin content was reduced by about 70%, and the proportion of proinsulin-related peptides increased from 18% to 38%. In the in vivo situation, pancreatic extracts from nonfasted diabetic Psammomys contained 36% proinsulin-related peptides in contrast to 15% in pancreatic extracts from nondiabetic animals. Thus, prolonged in vitro exposure of prediabetic Psammomys islets to high levels of glucose could reproduce the modified beta-cell secretory profiles observed in vivo in the diabetic animal. These results support the hypothesis that hyperproinsulinemia in NIDDM is secondary to the inability of beta-cells to meet a sustained increase in insulin demand, whereas individuals with normal beta-cells may meet such demand with an adequate output of mature insulin.

Perpendicular-incidence photometric ellipsometry of biaxial anisotropic thin films

A new measurement technique for the characterization of uniaxial as well as biaxial anisotropic surfaces and thin films is introduced. This technique is based on perpendicular-incidence photometric ellipsometry, in which a spectral-photometric dynamic ellipsometer with a rotating polarizer is used. This method is sensitive, contactless, nondestructive, and efficient for the estimation of anisotropic behavior. Furthermore, the spectroscopic measurement directly provides the anisotropy dispersion down to the UV wavelength range. Results on structurally anisotropic HfO(2) coatings are presented.

Laser conditioning of LaF(3)/MgF(2) dielectric coatings at 248 nm

Highly reflective LaF(3)/MgF(2) systems for a wavelength of 248 nm on MgF(2) and crystalline quartz substrates were investigated. The influence of laser conditioning on damage threshold and absorptance was remarkable in those coatings that had a high initial absorptance. Monitoring with a laser calorimeter revealed the conditioning effect to be a function of the irradiation dose rather than of energy density or pulse rate. Furthermore, x-ray photoelectron spectroscopy and transmission electron microscopy investigations showed that conditioning induces stoichiometric and structural changes in the multilayers, especially in near-surface sublayers, whereas scanning electron microscopy and atomic force microscopy investigations indicated that the surface remains unchanged.

Regulation by metformin of the hexose transport system in vascular endothelial and smooth muscle cells

1. The effect of the biguanide metformin on hexose transport activity was studied in bovine cultured aortic endothelial (BEC) and smooth muscle cells (BSMC). 2. Metformin elevated the rate of hexose transport determined with 2-deoxyglucose (2DG) in a dose- and time-dependent manner in both cell types. Similar ED50 values (0.8-1.0 mM) were determined for the effect of metformin on 2DG uptake in both BEC and BSMC following 24 h exposure to increasing concentrations of metformin, with maximal stimulation at 2 mM. 3. In BEC, metformin increased the hexose transport rate 2-3 fold at all glucose concentrations tested (3.3-22.2 mM). In BSMC incubated with 22.2 mM glucose, metformin elevated the hexose transport approximately 2 fold. The drug was also effective at lower glucose levels, but did not exceed the maximal transport rate observed in glucose-deprived cells. 4. Similar results were obtained when the effect of metformin on hexose transport activity was assessed with the non-metabolizable hexose analogue, 3-O-methylglucose, suggesting that the drug affects primarily the rate of hexose transport rather than its subsequent phosphorylation. 5. The metformin-induced increase in hexose transport in BSMC treated for 24 h with the drug correlated with increased abundance of GLUT1 protein in the plasma membrane, as determined by Western blot analysis. 6. These data indicate that in addition to its known effects on hexose metabolism in insulin responsive tissues, metformin also affects the hexose transport system in vascular cells. This may contribute to its blood glucose lowering capacity in patients with Type 2, non-insulin-dependent diabetes mellitus.

Hyperproinsulinemia in the diabetic Psammomys obesus is a result of increased secretory demand on the beta-cell

We have recently shown that the diabetic syndrome in Psammomys obesus is characterized by severe depletion of islet immunoreactive insulin (IRI) stores together with a marked increase in the islet proinsulin to insulin ratio. In the present in vitro studies, we show marked enhancement of proinsulin biosynthesis in islets from diabetic P. obesus (approximately 8-fold compared to nondiabetic islets). Proinsulin to insulin conversion and insulin degradation do not differ significantly between diabetic and nondiabetic islets. The rate of IRI secretion at a stimulatory concentration of glucose (16.7 mM) is comparable in diabetic and nondiabetic animals, but at a nonstimulatory glucose concentration (0 mM), islets obtained from diabetic animals show significant IRI release. beta-Cells from diabetic P. obesus also exhibited increased secretion of newly synthesized proinsulin and conversion intermediates under stimulatory conditions. Moreover, a novel secretory compartment, highly enriched in newly synthesized C peptide, characterized the beta-cells of diabetic animals. Our data suggest that the marked insulin depletion observed in diabetic islets is probably due to a hyperglycemia-driven increase in secretory demand that is not met by the enhanced biosynthetic capacity of these islets. This leads to relative enrichment of the depleted diabetic islets with immature secretory granules of a higher proinsulin content.

Insulin secretion in obese and non-obese NIDDM

Both the insulin response to glucose and the sensitivity to insulin show large variation in the normal population. Many subjects have either a markedly low insulin response or low sensitivity to insulin, with nevertheless normal glucose tolerance. For such subjects to become diabetic, insulin secretion or insulin action must further deteriorate with time, or other factors are added which tip the balance towards diabetes. Most evidence to date indicates that reduced beta-cell responsiveness and reduced insulin sensitivity co-exist in subjects prior to developing NIDDM. Both insulin secretion and insulin action are genetically controlled and influenced by intrauterine and neonatal factors. Insulin secretion and insulin action vary inversely in a closely linked manner; inability to fully compensate for changes in one variable may generate a functional deficit in glucose homeostasis. Subjects combining low functions would run a proportionately larger risk of decompensating the glucose tolerance and be more vulnerable, in terms of diabetes susceptibility, to factors that further reduce insulin output or insulin action. Careful analysis of existing data prompts us to ascribe a dominating role to the impairment of insulin secretion in the pathogenesis of IGT and NIDDM. Patients with NIDDM also exhibit increased proportions of proinsulin and proinsulin conversion intermediates. We used hyperinsulinaemic diabetic and non-diabetic Psammomys obesus to study the possible relationship between steady-state pancreatic insulin stores and the proportion of proinsulin-related peptides in the plasma and the pancreas. A marked increase in these peptides was associated with 90% reduction in insulin stores of the pancreas. After food deprivation, the depletion of pancreatic insulin in the diabetic animals was partially corrected, and the proinsulin/insulin ratio normalized. In contrast, non-diabetic psammomys showed only 50% reduction in pancreatic insulin stores under non-fasting conditions, with no change in proinsulin/insulin ratio. These findings suggest that in the diabetic Psammomys obesus, pancreatic capacity for storage/production of insulin is limited; the metabolic consequences of this limitation are amplified by increased secretory demand secondary to insulin resistance, thus facilitating the establishment of hyperglycaemia, which may in itself further exacerbate the pancreatic dysfunction.

Recombinant mapping of the familial hyperinsulinism gene to an 0.8 cM region on chromosome 11p15.1 and demonstration of a founder effect in Ashkenazi Jews

A gene for autosomal recessive familial hyperinsulinism (HI) (OMIM: 256450), a neonatal metabolic disease characterized by inappropriate insulin secretion in the presence of severe hypoglycemia, was recently mapped to a 6.6 cM interval between the markers D11S926 and D11S928 on chromosome 11p in 15 families (1). In the current study we evaluated six additional families and five new markers, and further localized the gene between D11S419 and D11S1310. Using genotype data from CEPH Version 7 and data generated from this study, this region was estimated to be 0.8 cM in length. Significant linkage disequilibrium between markers and the HI gene was observed over a region of 10.3 cM (11 pter-D11S926-D11S1308-11pcen) for Ashkenazi Jewish chromosomes. Haplotype analysis showed that 12 of 36 HI chromosomes, versus one of 36 non-HI chromosomes, bore a specific haplotype for D11S419-D11S902-D11S921 (p < 0.0007), strongly suggesting a founder effect in this ethnic group.

Influence of the xanthine derivative denbufylline and the anti-inflammatory agent nabumetone on microsomal free radical production and lipid peroxidation in rat liver

The influence of denbufylline, nabumetone and its main metabolite BRL 10,720 on iron stimulated lipid peroxidation (LPO), cytochrome P 450 dependent H2O2 and chemiluminescence (CL) production was investigated in rat liver microsomes in vitro (10(-5)-10(-3) M) and in vivo after treatment of rats (5-300 mg/kg b.m. orally on three consecutive days). In rat liver slices the release of thiobarbituric acid reactants (TBAR) was measured after 1 hour of incubation with the drugs. Denbufylline, nabumetone and BRL 10,720 exerted a significant inhibition of iron stimulated LPO in vitro. Nabumetone showed the strongest antioxidative activity, which was also seen in liver slices. These antioxidative effects were not found after in vivo treatment of rats. Denbufylline (10(-3) M) additionally inhibited H2O2 formation and the luminol and lucigenin amplified CL in vitro. Unexpectedly, nabumetone increased H2O2 formation both in vitro and in vivo, but in vitro only lucigenin amplified CL. BRL 10,720 increased microsomal H2O2 production in vivo. Moreover, BRL 10,720 enhanced CL in vitro and in vivo significantly, which is interpreted as an increase of the production of superoxide anion radicals and other reactive oxygen species such as H2O2, but lipid peroxidation in liver microsomes was not enhanced. These results suggest that denbufylline, nabumetone and BRL 10,720 in contrast to the in vitro effects did not exert antioxidative activities after treatment of rats. On the contrary, BRL 10,720 was found to support the formation of reactive oxygen species in liver microsomes.

Hyperproinsulinemia and insulin deficiency in the diabetic Psammomys obesus

Patients with noninsulin-dependent diabetes mellitus exhibit increased proportions of plasma proinsulin and proinsulin conversion intermediates. We used hyperinsulinemic diabetic and nondiabetic Psammomys obesus to study the possible relationship between steady state pancreatic insulin stores and the proportion of proinsulin-related peptides in the plasma and pancreas. Insulin-like peptides were separated by reverse phase HPLC and identified by pulse-chase experiments. A marked increase in the proportions of proinsulin and proinsulin conversion intermediates in the plasma and pancreas of diabetic nonfasted Psammomys was associated with 90% reduction in insulin stores of the pancreas. After a 16- to 20-h fast, the depletion of pancreatic insulin in the diabetic animals was partially corrected, and the proinsulin/insulin ratio was normalized. In contrast, nondiabetic Psammomys showed only 50% reduction in pancreatic insulin stores under nonfasting conditions, with no change in the proinsulin/insulin ratio. These findings suggest that in the diabetic Psammomys obesus, the pancreatic capacity for storage of insulin may be limited; the metabolic consequences of this limitation are amplified by increased secretory demand secondary to insulin resistance, thus facilitating the establishment of hyperglycemia, which may in itself further exacerbate pancreatic dysfunction.

Familial hyperinsulinism maps to chromosome 11p14-15.1, 30 cM centromeric to the insulin gene

Familial hyperinsulinism (HI) is the most common cause of persistent neonatal hyperinsulinaemic hypoglycemia. Linkage analysis in 15 families (12 Ashkenazi Jewish, 2 consanguineous Arab, 1 non-Jewish Caucasian) mapped HI to chromosome 11p14-15.1 (lod score = 9.5, theta = 0 at D11S921). Recombinants localized the disease locus to the 6.6 cM interval between D11S926 and D11S928. In Jewish families, association (p = 0.003) with specific D11S921/D11S419 haplotypes suggested a founder effect. This locus, which is important for normal glucose-regulated insulin secretion, represents a candidate gene for studies of other diseases of beta-cell dysfunction including non-insulin-dependent diabetes mellitus (NIDDM).

Replication of adult pancreatic-beta cells cultured on bovine corneal endothelial cell extracellular matrix

A valuable system has been developed to study replication of adult beta cells. Isolated islets from adult rats were partially dispersed and plated on dishes coated with extracellular matrix from bovine-corneal endothelial cells. Within 24 h islet cells attached to the matrix and formed a monolayer. The proportion of insulin-, glucagon-, and somatostatin-containing cells in the cultures was characteristic of whole islets. Function of beta cells was assessed by measuring glucose-stimulated insulin release. Insulin release from 7-day-old cultures increased 19-fold after a 16.7 mM glucose challenge indicating that beta-cell function was normal. Cellular replication in the cultures was assessed using the thymidine analogue 5-bromo-2'-deoxyuridine (BrdU). BrdU incorporation was noted in insulin-, glucagon-, and somatostatin-containing cells and also in non-endocrine cells. Among endocrine cells, the majority of BrdU labeling occurred in beta cells. Beta-cell replication potential was assessed using different concentrations of glucose. The incorporation of BrdU into beta cells was affected in a dose-dependent manner by glucose; over a 10-fold increase of beta-cell BrdU labeling was observed when glucose concentration was raised from 5.5 to 16.7 mM. The system proved advantageous for studying the replication potential of adult beta cells.

Differential regulation of glucose transport and transporters by glucose in vascular endothelial and smooth muscle cells

Hyperglycemia has been implicated in the pathogenesis of both micro- and macrovascular complications in diabetes. Little is known, however, about glucose transporters and their regulation in the vascular system. In this study, the regulation of glucose transporters by glucose was examined in cultured BAECs and BSMCs, and in human arterial smooth muscle cells. Both BAECs and BSMCs transported glucose via the facilitated diffusion transport system. Glucose-transport activity in vascular smooth muscle cells was inversely and reversibly regulated by glucose. Exposure of BSMCs and HSMCs to high glucose decreased Vmax for 2DG and 3-O-MG uptake, whereas Km remained unchanged. The hexose-transport system of BAECs exhibited lower 2DG and 3-O-MG uptake compared with BSMCs and showed little or no adaptation to changes in ambient glucose. Northern blot analysis demonstrated that GLUT1 mRNA levels in BAECs and BSMCs were unaffected by the concentration of glucose in the medium. GLUT2-5 mRNA could not be detected by Northern blot analysis. GLUT1 protein, quantified by Western blot analysis, was more abundant in BSMCs than in BAECs and was decreased by approximately 50% when medium glucose was elevated from 1.2 to 22 mM for 24 h. The alterations in the level of GLUT1 protein correlated with the changes observed in transport activity. These observations suggest differential regulation of glucose transporter in response to glucose between smooth muscle and endothelial cells. The sites of autoregulation may involve translational control and/or the stability of the protein in the smooth muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiocontrast agents induce endothelin release in vivo and in vitro

The intravascular administration of the ionic radiocontrast agent sodium iothalamate (2.9 g of iodine/kg body wt) to rats induced an increase in plasma concentration of immunoreactive endothelin from 21.3 +/- 1.2 to 36 +/- 3 fmol/mL, preceded by a transient rise in the plasma level of atrial natriuretic peptide and associated with a fall in RBF. Equi-iodine amounts of the nonionic agents ioxaglate and iohexol elicited similar or more marked changes in plasma endothelin, but hypertonic solutions of NaCl, mannitol, or glucose did not. Comparable levels of endothelin produced by infusions of endothelin-1 induced a reduction of up to 29% in RBF. Iothalamate and iohexol stimulated endothelin release from cultured bovine endothelial cells, suggesting a direct effect of ionic and nonionic agents on vascular endothelium. The data invite speculation that under some circumstances endothelin release might play a role in the circulatory changes caused by these compounds and in the pathogenesis of radiocontrast nephropathy.

In-vivo and in-vitro studies on the effect of amphotericin B on endothelin release

Since amphotericin B nephrotoxicity is mediated, in part by hypoxic tubular injury, the role of endothelin in the renal vasoconstriction, characteristic of amphotericin toxicity has been studied. Intact and salt depleted rats were infused with amphotericin B (20 micrograms/kg per min) or 5% dextrose over 20 min. Plasma endothelin levels determined at the conclusion of the infusion period, did not differ between the experimental groups, despite a marked reduction in renal blood flow noted in rats infused with amphotericin B. Amphotericin B (10(-5)-10(-7) M) did not stimulate endothelin release from cultured bovine aortic endothelial cells. However, in a model of chronic amphotericin nephrotoxicity produced by repeated daily intraperitoneal injections of amphotericin B (5 mg/kg) to salt depleted rats, renal failure was associated with elevated plasma endothelin levels (29.3 +/- 4.4 fmol/mL, vs 10.8 +/- 1.2 fmol/mL in salt depleted controls, P less than 0.01). We conclude that while plasma endothelin may be increased in chronic amphotericin B nephropathy, this peptide does not mediate the acute renal vasoconstriction associated with the infusion of this drug.

Monolayer culture of adult rat pancreatic islets on extracellular matrix: modulation of B-cell function by chronic exposure to high glucose

Studies in vivo indicate that chronic hyperglycemia is deleterious for insulin secretion. We have used an improved islet monolayer culture system to study chronic modulations of B-cell function. Adult rat islets maintained over several weeks on extracellular matrix in the presence of 11.1 mM glucose responded to an acute stimulation with 16.7 mM glucose by a 5- to 8-fold increase in insulin secretion. When cultured in the presence of higher glucose concentrations, the response to an acute glucose stimulus diminished time and dose dependently. In islets desensitized by exposure to 33.3 mM glucose for 1 week, reduction of the glucose level to 11.1 mM reversed the desensitization within 2 weeks. This desensitization was not limited to the glucose stimulus; responses to other nutrient secretagogues, such as glyceraldehyde and alpha-ketoisocaproic acid, were also reduced. In contrast, responses of insulin secretion to nonnutrient stimulators (tolbutamide and quinine) and amplifiers (isobutylmethylxanthine and carbachol) showed no desensitization in islets exposed to 33.3 mM glucose. Desensitization similar to that caused by 33.3 mM glucose could be induced by 11.1 mM glucose together with 0.1 mM isobutylmethylxanthine. High glucose also caused a time-dependent loss in compact monolayer organization with disruption of cell contacts. Our studies suggest that 1) generation of the reduced insulin response may be related to the prolonged high insulin secretion rate; 2) expression of the functional change is specific to the nutrient stimulus-secretion coupling; and 3) modifications in intercellular contacts may be involved in B-cell desensitization.

Regulation of insulin release in persistent hyperinsulinaemic hypoglycaemia of infancy studied in long-term culture of pancreatic tissue

Pancreatic tissue was obtained during therapeutic subtotal pancreatectomy from five infants with persistent hyperinsulinaemic hypoglycaemia of infancy (so-called nesidioblastosis). Collagenase digests of the specimens were cultured in RPMI 1640 medium on extracellular matrix-coated plates. Acute insulin secretion showed minimal sensitivity to changes in glucose concentration. Sensitivity to other nutrient secretagogues such as glyceraldehyde, leucine, alpha-ketoisocaproic acid and arginine was variable, showing either diminished or absent response. On the other hand, stimulators of Beta cell cAMP and modulators of the phosphoinositide-protein kinase C pathway were effective inducers of insulin release. The response to cAMP stimulators was independent of the glucose concentration. Although insulin output was high in the absence of glucose, this was not due to passive leak of hormone, since both removal of calcium and addition of somatostatin and epinephrine inhibited the secretion. Beta cells were more sensitive to somatostatin than epinephrine; however, both agents failed to completely suppress the release even at suprapharmacological concentrations. Although it cannot be excluded that the culture conditions affected Beta cell function, the present findings may suggest that cultured Beta cells in persistent hyperinsulinaemic hypoglycaemia of infancy behave like fetal Beta cells at early developmental stages.